1. Field of the Invention
This invention relates to a mounting structure for a heat sink onto an integrated circuit package mounted on a printed circuit board.
2. Description of the Related Art
In recent years, portable electronic apparatus such as, for example, lap-top personal computers, appear widely on the market as electronic apparatus for which miniaturization and high reliability are required. In order to achieve a high performance of electronic apparatus of the type mentioned, it is necessary to use one or more integrated circuit packages having a great amount of heat generation. Therefore, in order to assure a heat radiation property of an integrated circuit package having a great amount of heat generation, a heat sink is used when an integrated circuit package is to be mounted onto a printed circuit board. A heat sink is required to be mounted such that it closely contacts, with certainty, a heat radiation face of an integrated circuit package in order to prevent an increase of the heat resistance by contact, to optimize the mounting structure for a heat sink onto an integrated circuit package.
FIG. 17A is a top plan view of a conventional mounting structure for a heat sink onto an integrated circuit package, and FIG. 17B is a side elevational view of the same. In the present conventional example, an integrated circuit package 101 is mounted in a little floating condition on a printed circuit board 103 by soldering pins 102 of the integrated circuit package 101 to a conductor pattern (not shown) of the printed circuit board 103, while depressions 106 are provided at upper face edge portions of a heat sink 105 having heat radiation fins 104, and the heat sink 105 and the integrated circuit package 101 are held at the depressions 106 of the sink 105 and lower face edge portions of the integrated circuit package 101 by clips 107 having a substantially C-shaped section and made of a resin or the like (refer to, for example, U.S. Pat. No. 5,099,550).
FIG. 18A is a top plan view of another conventional mounting structure for a heat sink onto an integrated circuit package, and FIG. 18B is a side elevational view of the same. In the present conventional example, pins 112 of an integrated circuit package 111 are mounted on a printed circuit board 114 by way of a frame 113 made of an insulator such as a resin. The frame 113, having a substantially rectangular shape as viewed in plan, has a pair of projections 115 which project sidewardly at locations in the proximity of a diagonal line of an upper face thereof. A heat sink 117 having heat radiation fins 116 at an upper portion thereof is placed on an upper face of the integrated circuit chip 111, and a clip 118 formed from a metal wire shaped in a crank shape is disposed on the heat sink 117 while the opposite ends of the clip 118 are engaged with the projections 115 of the frame 113 so that the heat sink 117 is fixed relative to the integrated circuit package 111 (refer to Japanese Patent Laid-Open Application No. Showa 63-133557 or U.S. Pat. No. 4,745,456).
In the conventional example described with reference to FIGS. 17A and 17B, since the upper face edge portions of the heat radiation fin 105 are held by means of the clips 107 having a C-shaped section, it is necessary to provide the depressions 105 of a comparatively large size at the edge portions, and there is a problem in that the heat radiation area of the heat sink 105 is decreased and the cooling efficiency is deteriorated.
Meanwhile, in the conventional example described with reference to FIGS. 18A and 18B, since it is necessary to interpose, already at the stage when the integrated circuit package 111 is to be mounted onto the printed circuit board 114, the frame 113 between the integrated circuit package 111 and the printed circuit board 114, there is a problem in that the manufacturing operability is low. Further, when the frame 113 made of a resin or the like is broken, for example, at a portion of a projection 115, it is difficult to exchange the frame 113, and the heat sink 117 can no longer be mounted.